Heat transfer units for internal combustion engines have been described in a number of patent applications. They serve both to cool gases, such as charge air or exhaust gas, and to cool liquids, such as oil.
Not least because of the various fields of application, very different structures of heat transfer systems are known. Examples include tubular coolers, plate-like coolers and die-cast coolers.
Excess sooting of the channels through which exhaust gases flow should be prevented when cooling exhaust gases, so that the cross section of the channels should not be chosen to be too small. In order to still provide a sufficiently good heat transfer, coolers, such as coolers made by a die-cast process, have been developed in which ribs extend into the channel through which the fluid to be cooled flows, said ribs extending from the partition walls between a channel through which the cooling fluid flows and a channel through which the fluid to be cooled flows. These ribs in particular improve heat transfer with high temperature gradients.
DE 20 2006 009 464 U1 describes a heat exchanger comprising an inner and an outer shell, with the channel through which the coolant flows being formed in the inner housing of the heat exchanger, and wherein this channel is enclosed by a channel through which exhaust gas flows, into which ribs extend and which is arranged between the inner and the outer shell. Ribs extend into the channel from the partition wall between the two channels, which ribs extend over the entire length of the channel through which the fluid flows. The ribs are arranged in successive rows and each has a onflow edge joined by two side walls, the angle between the two tangents to each side wall of the ribs decreasing continuously in a front portion until the enclosed angle is 0°, and the two side walls thus extending parallel to each other in a rear portion. Both side walls end at a respective onflow edge at the end of each rib so that a right angle is formed between a rear wall of each rib and the side walls. Good heat transfer, and thus a high cooling capacity, is thereby achieved.
A heat exchanger having a rib design is also described in DE 10 2006 029 043 A1. This heat exchanger is also composed of an outer shell and an inner shell that serves as a partition wall between an inner, exhaust gas conveying channel, into which the ribs extend, and an outer, coolant conveying channel which is arranged between the inner and the outer shell. The cross section through which exhaust gas can flow is reduced over the flow path according to the reduced density of the exhaust gas in order to realize an improved cooling capacity and a lower pressure loss. Due to the higher flow velocity in the outlet region, the insulating boundary layers are reduced whereby the cooling capacity is increased. However, the reduced free cross section between the ribs result in increased sooting, particularly with colder exhaust gas, so that the efficiency of the cooler decreases.
Various rib shapes differing in width, length, height and overlap are also described in DE 10 2004 045 923 A1. These are either ribs of constant cross section or ribs with two opposite wings. These serve to improve heat transfer capability with only a slight increase in pressure loss. Heat transfer devices having one of the embodiments described above have limited efficiency, since no adjustment is made with respect to different temperature gradients and to the resulting different sooting tendencies.